The increased variety and sophistication of devices employed in telecommunication industry has served to highlight the need to provide devices capable of interacting with electromagnetic waves, such as lightweight antennas, lens, absorbers, concentrators, and so on. This need is especially critical with respect to the low frequency band of the electromagnetic spectrum, such as radio frequency, and over a broad band of other frequencies, typically ranging from 100 KHz to 100 GHZ.
It will be desirable therefore to design a material which, during initial manufacture, can be optimized for a particular application and wave frequency, especially, low frequency suitable for radio transmission. While such broadband absorbers and antennas have hitherto been produced, they are typically quite bulky, heavy, and generally ill-suited for operational use in those situations where low bulk and light weight are of paramount importance. Furthermore, even with absorbers satisfying both low bulk and low weight requirements, it often turns out that the absorber construction is so complex as to render impractical its production in an economical manner.
Thus, bulk absorbers are commonly used for absorbing radiation. A bulk absorber has varying particle concentrations throughout the absorber, which alter the dielectric or magnetic properties of the absorber. The particle concentrations can be designed to absorb target waves, depending on the application.
McDonnell Douglas Helicopter, Co, U.S. Pat. No. 6,406,783 A, 18.06.02 describe a bulk radiation absorber having altered dielectric or magnetic properties, and more specifically, bulk absorbers with predetermined concentration gradients. The particle concentrations can be selected to absorb target waves, depending on the application. The bulk absorber comprises particles dispersed throughout the matrix in a substantially continuous concentration gradient. The particles have dielectric or magnetic altering properties. The particles may be carbon fibers, coated hollow microspheres, carbon black, carbon whiskers, or a combination thereof. The matrix may comprise foam materials or ceramic materials. The foam material may be syntactic or blown foam, and may be thermoplastic or thermoset.
Another area of practical interest for potential application of materials embedded with nanoparticles includes lens, antennas and concentrators.
Described by Raytheon Company; U.S. Pat. No. 6,788,273; 07.09.2004 is a compensated radome, comprising an inner layer of a negative index of refraction material, often referred to as a “metamaterial”, and an outer layer of a positive index of refraction material. The thickness of the two materials and their respective refractive indices are adjusted so that a beam of light passing through the radome is effectively not refracted. The metamaterial-compensated radomes solve the bore sight angle problem with a minimum of complexity. Disclosed by Alcatel, U.S. Pat. No. 6,229,500, 08.05.01 is a multilayer focusing spherical lens adapted to be mounted in a transceiver antenna device of a terminal of a remote transceiver system and having a concentric focal sphere, the lens including a central layer and a peripheral layer having different dielectric constants, each dielectric constant value being determined so that the lens focuses parallel microwave beams towards the focal sphere concentric with the lens.
Disclosed by Southwest Research Institute, U.S. Pat. No. 6,249,261, 19.06.01 is the direction-finding antenna constructed from polymer composite materials which are electrically conductive, with the polymer composite materials replacing traditional metal materials. An inherent advantage of replacing metal materials is significantly lower radar reflectivity (radar cross section) and lower weight. The reduced radar reflectivity reduces the range of detectability of the antenna by possible adversaries. Despite significantly lower radar reflectivity, the antenna assembly has direction-finding characteristics which are essentially equivalent to traditional metal antennas.
Disclosed by International Business Machines Corporation, U.S. Pat. No. 6,271,793, 07.08.01 is the RF antenna made from a composite material, wherein the composite material preferably comprises electrically conducting particles in a matrix, and wherein the electrically conducting particles have such a high density that the electrical conductivity of the composite material is large enough for the antenna to receive RF signals sufficient to activate the RF tag.
There are numerous disadvantages to the prior art bulk absorbers, lens and concentrators with a discontinuous dielectric or magnetic altering property gradient. The discontinuities in these materials, due to the step-wise changes in the dielectric or magnetic altering property gradient, cause deflection or reflection of the waves that are meant to be focused or, opposite, absorbed. Additionally, the bond layer in between the adjacent billets also causes possible deflection or reflection of the waves.
Lately, various novel methods of manufacturing composite lightweight materials useful as a waveguide, lens or wave absorbers were reported.
Thus, disclosed by FDC Corporation, JP2004182545; 02.07.2004 is a method of manufacturing porous ferrite by which firing free from breaking or crack is carried out and vacancy is properly formed in a sintered compact and a radio wave absorber having radio wave absorption characteristic capable of making frequency high and wide by making porous and having excellent mechanical strengths and weather resistance. The method of manufacturing the porous ferrite is performed by measuring ferrite powder of a base material, previously firing at a prescribed temperature, pulverizing the previously fired body and granulating, mixing a fine organic material particle and a thermoplastic powder having low melting point and binder function with the previously fired ferrite powder, molding and firing to eliminate the additive components to obtain the porous sintered compact. The organic material particle (starch) and the thermoplastic powder (paraffin fine particle) are added by 0-30 wt. % in total and the mixing ratio of the organic material particle is increased in a ratio ranging from 0 to 5 wt. % with the increase of the thermoplastic powder. When the thickness of a sample (d) is 0.8 cm, the return loss in about 100-750 MHz is ≧20 dB to cope with VHF-UHF whole band.
As ferrite fine particles may be used magnetic fine particles, such as a NiZn system, a MgZn system, and a MnZn system.
Disclosed by Viktor A. Podolsky and Evgueni E. Narimanov; US 2006/0257090; 16.11.2006 is a waveguide structure comprising a first and a second waveguide border elements having substantially planar surfaces and a core material therebetween having a positive in-plane dielectric constant and a negative perpendicular-to-plane dielectric constant, wherein the waveguide structure exhibit a negative index of refraction for electromagnetic radiation in a frequency range, such as from 1 GHz to 1 mln GHz or in the wavelength range of about 1×10−7 Hz to 1×10−1 m. The core material can comprise inclusions having a negative dielectric constant embedded in a host material having a positive dielectric constant. The inclusions can be distributed substantially homogenously in a host medium. In addition to the embodiments described above having nanowires embedded in a dielectric host, other composites having inclusions embedded in a host material can be used to achieve the desired left-handed optical characteristics. For example, randomly distributed inclusions (e.g., nanoparticles) with a negative dielectric constant and having a variety of shapes can be embedded into a transparent dielectric host having a positive dielectric constant. The negative e in these embodiments can be achieved both in optical and infrared frequency ranges by using plasmonic (e.g., Ag, Au, and the like) or polar (e.g., SiC, and the like) materials to at least partially form the inclusions.
Paul D. Zwick, in US 2002/0049276, 25.04.2002 describes thermoplastic elastomer gel composition and method of making same. The thermoplastic elastomer gel composition can comprise a variety of magnetic additives. Typically, these additives are ferrite complexes, which when charged or energized by another strongly magnetic force, will become magnetic or dipolar and yield magnetic fields. Strontium and Barium Ferrite are the most common commercially used ferrites, but other ferrites can also be used. The magnetic additives require additional manufacturing steps. Specifically, after being formed or extruded the gel containing the magnetic ingredients should be oriented through a powerful magnetic field. However, specific details of how the orientation can be implemented are not disclosed.
Therefore, it would be advantageous to obtain a low bulk lightweight material having properties which can be modified during manufacture targeting a specific application in a particular waveband range.
Further, there would be advantageous to obtain a low bulk lightweight material fabricated such as to reduce the wave distortions due to discontinuous dielectric or magnetic property gradients.
In view of the foregoing, it is an object of the present invention to provide an electromagnetic radiation absorber having both low bulk and low weight.
A still further object of the present invention is to provide an electromagnetic radiation absorber useful for dissemination of electromagnetic radiation of a given waveband range.
Yet another object of the present invention is to provide an electromagnetic radiation absorber which is sufficiently flexible and if desired, can be configured during manufacture around the object to assume the contours of the object.
A still further object of the present invention is to provide an electromagnetic radiation absorber which may be molded or otherwise shaped to permanently assume virtually any predetermined geometrical configuration.
A still further object of the present invention is to provide an electromagnetic radiation absorber which is useful over a relatively large portion of the electromagnetic radiation spectrum, which is of simplified construction, easy to produce and which is adapted for manufacture in an economical manner.
Another object of the present invention is to provide a simplified method for producing an electromagnetic radiation absorber which satisfies the above-stated general objects and others.